Bill Esterson, whose constituency covers areas including Crosby, Formby, Maghull and Aintree, said: “Cuts to disabled people of £3,500 a year were a key part of Chancellor George Osborne’s budget last week.

“They were agreed by Iain Duncan Smith as the Secretary of State for Work and Pensions. Mr Duncan Smith resigned after the government had announced that it was backing down, saying he had been against the cuts all along.

“Everything about these cuts is shameful. There is no moral, political or economic case for targeting disabled people in this manner. It is clear that George Osborne’s budget robbed some of the poorest in our country to give to some of the richest.

Sefton Central Labour MP and new shadow minister for small business Bill Esterson

“Iain Duncan Smith has introduced the Bedroom Tax; he has overseen the Work Capability Assessment; cut support from cancer patients; and cut the benefits of people who want to do work experience to improve their job prospects, not provide slave labour.

“This is a man who has been responsible for some of the nastiest policies of the nastiest of Conservative governments, all with the support of the Liberal Democrats for five years.

“It beggars belief that he has suddenly discovered a conscience, not least when the cuts he objected to had been suggested by him and had been withdrawn before he resigned.

“Iain Duncan Smith’s resignation is not about protecting disabled people.

“It is about a battle for the future of the Conservative Party and it is at the expense of disabled people in this country.”

Prime Minister David Cameron said yesterday that he was “puzzled and disappointed” at Iain Duncan Smith’s resignation.

Earlier, the government had indicated it would look again at some of the proposed disability benefits changes.